1. Field of the Invention
The present invention relates generally to private branch exchanges (PBX), key system units (KSU) and the like systems. In particular, it relates to novel, distributed systems, especially utilizing the internet protocol (IP) and wideband data links such as Ethernet, Token Ring or the like channels.
2. Background of the Invention
A traditional time-division multiplex (TDM) PBX is a centralized unit with voice trunks connecting it to the telephony central (switching) office (CO) and local station circuits interconnecting it to the station terminals. Such PBX systems may be expanded by adding trunk and station expansion units. It may have additional telephony applications, provided by means of a co-located server interconnected with the centralized unit through a proprietary interface protocol, such as voice mail, call centre, interactive voice response or computer telephony integration.
Such PBX and KSU systems are normally used by commercial enterprises, which often have several offices and locations, which makes it cumbersome to efficiently employ, reconfigure or expand the centralized systems.
The present invention enables a distributed system to be employed throughout an entity""s offices and locations, reducing initial and continuing costs by focusing subcomponents interconnection in a standard transmission medium (such as Ethernet) and protocol (such as IP or Novell""s IPX). This also facilities consolidation and integration of the system within the wide area network (WAN).
A distributed PBX, KSU and the like system according to the present invention has at least one time domain multiplexed (TDM) switch unit interfaced with transparent wideband channels such as Ethernet by means of at least one Public Switched Telephone Network (PSTN) interface unit and at least one service module (SM) interconnecting it to remote station terminals. One or more applications servers may be located where available or convenient and interact with the TDM switch unit by means of IP addressable path or paths.
An advantage of the above mentioned system is that it need not carry timing information for purposes of synchronization, which is therefore achieved in the preferred implementation by using the data cell/packet departure and arrival rates between the TDM switch and the TDM peripherals.
A more general advantage of the present system is that entities may utilize both traditional PSTN and the IP network for voice communication with seamless and transparent transition between them to the user. It is therefore possible to use advanced features such as paging, call forwarding/transfer, agent queuing and other advanced features in an IP distributed environment. For a geographically distributed organization the cost of implementation is significantly lower than previously.